Generally, when a patient is under a local anaesthetic it is desirable to monitor oxygen and carbon dioxide levels in the exhaled air. This is done by providing a small tubular element or conduit leading from within the respiratory face mask and through same to its exterior, and thereby directing a portion of the stream of air exhaled by the patient to a suitable apparatus for measuring the components thereof, such as a mass spectrometer or capnograph.
It is the current practice of the profession to pierce the face mask with a needle catheter in a region thereof so as to intersect the stream of exhaled air by the patient within the mask, which catheter is provided externally with a length of suitable tubing to conduct the exhaled air stream to the monitoring apparatus.
One disadvantage of this procedure can be readily appreciated; the catheter needle could inflict injury to the operating staff during the insertion or withdrawal process or otherwise, and to the patient as well.
Further, such needle-related injuries could be of particular concern to both medical staff and patients because of the possibility of the transmission of disease through any inflicted wound.
Other proposals have been put forward for utilizing a tube or conduit length with a respiratory face mask, such as by the method disclosed in U.S. Pat. No. 4,328,797. The invention disclosed by this patent, however, primarily deals with the introduction of a length of tube through the mask to be used for naso-gastric intubation procedures.
One disadvantage of such aforementioned proposal, if it were to be used for monitoring exhaled air, is that it does not contemplate or provide for precise placement of the tube end near the nostril of the patient and in a region for repeated requisite sampling of the exhaled air stream so as to obtain an accurate measurement of the oxygen and carbon dioxide levels therein.
Another disadvantage of the aforementioned respiratory face masks, is that the body of the face mask, when located on the face of the patient or wearer, extends over the nose to a region just below the level of the wearer's eyes. This is most unaccommodating to the variety of facial features of typical patients requiring use of such respiratory face masks, and in certain circumstances, the extreme forward end of the face mask impinges on the respective corners of the eyes of the patients.